Spark Gap generator can jam a wide variety of electronics. It's also illegal regardless of the intent.
It's a silly thing in America. If someone blatantly ignores no cell warning in hospital and the cell phone causes malfunction of the medicinal equipment, the person who depended on it can sue doctors for unsafe equipment. The doctor can try to sue the cell phone user for causing the damage, and the cell phone service for not making it safe to use in hospital.
Yet as you mentioned, jamming phone can also lead to lawsuit if they can't call 911 or something.
Know what I think should be done? Require cell phone provider to block and refuse non-911 cell phone call if the GPS reports them inside any medicinal facility that Goverment deems suseptible to cell phone interference.
Until then, the office could hire an ugly looking female secretary named Helga, and have her glare at anyone who uses cell phones in a no call area. Most people would get nervous when you have a 2000-lbs woman with unibrow and hairy moles bigger than an animal mole staring at you.